Data packet transmission in multipoint-to-multipoint networks (e.g., ad-hoc or mesh networks) is usually arranged by sending one or more data packets. A data packet is often encoded and modulated. Also, a data packet typically includes at least one frame. Each frame is preceded by a preamble. The primary purposes of the preamble include 1) enabling the receiver of the frame to detect the frame on the transmission medium, 2) adjusting the gain of the receiver (e.g., an analog front end (AFE)) and synchronizing the clock so that frame is received when expected. The frame also has a header that carries information helping the receiver to address, demodulate, and decode the frame.
Because of their ubiquitous nature, powerlines are increasing in popularity as a transmission medium for many networks. Unfortunately, powerlines are a notoriously noisy medium for data communications. Noise disturbs all parts of the data packet, including the preamble. If the noise erases or significantly damages the preamble or its parts, the entire data packet is usually lost. It is common for impulse noise, both instantaneous and repetitive, to damage the preamble enough to lose the packet. With regard to packet loss, repetitive impulse noise is the most insidious, because retransmission of the packet may not be sufficient to recover from the packet loss.
The conventional approaches to improve robustness of the preamble are typically effective for stationary noise (e.g., white Gaussian noise, WGN). The signals used in the preamble are selected to have high autocorrelation characteristics; thus, they could be recognized in the presence of a high amount of stationary noise.
So, conventional approaches to improve robustness of the preamble are ineffective for noisy communication media, like powerlines, that are characterized by non-stationary noise (e.g., impulse noise) rather than stationary noise.